The present invention generally relates to the manufacturing of surgical sutures that are stretchable and that have a porous structure, the suture being of the non-braided and non-woven type and having a surface porosity that provides an environment that is conducive to tissue ingrowth into the pores of the porous surface. The method includes forming the porous suture from a mixture of elastomeric polymer and elutable organic solvent materials, which mixture is extruded into the configuration of a strand or a suture, after which the extruded strand is passed through a trough or the like containing a liquid which elutes the organic solvent from the strand in order to form the porous surface of the stretchable suture.
Most sutures which are available today for the repair, fixation and/or approximation of body tissues during surgical procedures are composed of single strands or multiply braided strands of flexible material, with or without a needle attached to one or both ends of the flexible material. Sutures which are used for the attachment of prosthetic devices or implants to body tissues have especially stringent requirements regarding strength, biocompatibility, flexibility, sterilizability and, in some cases, biodegradability. An especially desirable property for sutures that are intended for specialized uses such as those involving biologic, synthetic or biosynthetic vascular grafts is to provide the suture with porosity that extends to the external surface of the suture and that provides for rapid tissue ingrowth and endothelialization, as well as other important properties. An example of a porous suture is found in MacGregor U.S. Pat. No. 4,712,553.
Providing prosthetic devices and implants with porous surfaces has been developed in order to promote the implantation of such devices. Porous coatings or surfaces have been implemented on or proposed in connection with devices such as heart valves, cardiac pacers and electrodes thereof, vascular grafts, blood pumps, ventricular assist devices, artificial hearts, flexible heart valve members, bloodstream filters, intracardiac patches, diaphragms or baffles, vascular access tubes, and the like. One of the objectives of providing porous surfaces on these types of devices and implants is to promote colonization and tissue ingrowth into the depth of the porous surface from adjacent body tissue in order to provide bonding between the body tissue host and the porous member. Typically, the body tissue ingrowth is combined with the promotion of tissue growth into the porous surface from the nucleated bloodstream cells. Such porous surfaces provide a porous depth that affords a means of fixation to host tissues by soft tissue growth into the porous depth of the surface, and they provide tissue-implant interfaces which are blood compatible arising from colonization and tissue formation on the blood-contacting surfaces.
Imparting stretching and porosity to sutures according to the present invention has been found to provide advantageous properties including exceptional compliance between the host tissue and the implant device or the like while simultaneously permitting body tissue ingrowth into the pores of the suture in order to accelerate the healing process. The property of exceptional compliance of the stretchable suture assists the suture in being able to yield to bending under stress conditions imparted by sewn and/or knotted suture assemblies. By allowing tissue ingrowth into the interstices of the porous suture, potential dead spaces are reduced or eliminated thus making the suture less prone to primary or secondary infection. The stretchable porous suture also provides the possibility for reduced intimal hyperplasia and stenotic narrowing at the anastomotic site. The generally compressible nature of the stretchable porous suture made according to the invention permits the use of a needle whose diameter is less than that of the suture itself in order to thereby reduce blood leakage at suture sites in vascular anastomoses.
Additionally, the elastomeric properties and surface irregularities that are associated with the stretchable porous suture structure according to this invention result in less slippage when the suture is tied in order to provide a more secure knot than that achieved by using smooth or monofilament sutures that are not elastomeric. The porous suture structure also provides a favored environment for the controlled release of drugs to promote healing and/or to resist infection. Porous stretchable sutures according to this invention can be made of the same material as, and be provided with a surface structure that is similar to, the device being implanted with the aid of the suture, such as a synthetic graft, with the result that the suture material will demonstrate substantially the same physical and chemical properties as the device being sutured. This can be of assistance in promoting more uniform healing because the surface free energy of the porous suture will be similar to that of the graft being secured thereby. If desirable, the porous suture can be bonded to the vascular graft or the like, which is facilitated when the suture and the graft are made of substantially the same material.
These various properties and advantages have been attained by the present invention, by which a non-braided stretchable surgical suture is provided which includes an exterior portion having a porous structure, such exterior portion being between the outer surface of the suture and a location internal thereof to provide a porous surface or layer. Manufacturing the porous stretchable suture includes elution from a continuous elongated polymeric member which exhibits substantial elastomeric properties when extruded into a strand from a combination of the polymer and an organic solvent for the polymer. The method includes eluting the organic solvent from the extruded strand by passing same through a liquid which leaches or elutes the organic solvent from the strand.
It is accordingly a general object of the present invention to provide a method for producing an improved surgical suture.
Another object of this invention is to provide a method for forming an improved surgical suture that has pores generally external thereof.
Another object of the present invention is to provide an improved method for forming a surgical suture that is of the non-braided, non-woven type, while still having compressible qualities for reducing blood leakage at suture sites in vascular anastomoses.
Another object of the present invention is to provide an improved method for extruding a surgical suture that permits body tissue ingrowth into an external portion thereof that provides a porous surface.
Another object of this invention is to provide an improved method for manufacturing a porous surgical suture for accelerating the healing process and for reducing the likelihood of primary or secondary infection.
Another object of the present invention is to provide an improved method for forming a surgical suture that can be made from the same material and can be provided with the same surface structure as a synthetic graft or the like that is being fixed in place by the suture.
Another object of this invention is to provide an improved method for forming a surgical suture provided with surface irregularities which lessen the likelihood of slippage when the suture is tied and which provide a favored environment for the controlled release of drugs to promote healing and/or to resist infection.
Another object of the present invention is to provide an improved method for providing a surgical suture that is stretchable, particularly in the axial direction.
Another object of this invention is to provide an improved manufacturing method for a surgical suture that exhibits improved matching or compliance between host tissue and a graft or the like.
These and other objects, features and advantages of this invention will be clearly understood through a consideration of the following detailed description.